1. Field of the Invention
A single mode optical waveguide fiber for use in telecommunication systems and more particularly, a waveguide fiber which reduces non-linear dispersion effects, combines bend resistance, low polarization mode dispersion (PMD), low attenuation, and large effective area features desired, for example, in underground and undersea applications is disclosed herein.
2. Technical Background
Optical amplifier technology and wavelength division multiplexing techniques are typically required in telecommunication systems that require high power transmissions for long distances. Undesirable non-linear effects become more pronounced for higher powers and/or longer distances. The definition of high power and long distances is most meaningful in the context of a particular telecommunication system wherein a bit rate, a bit error rate, a multiplexing scheme, and perhaps optical amplifiers are specified. Additional actors, known to those skilled in the art, have impacted upon the definition of high power and long distance. However, for most purposes, high power could be considered to be an optical power greater than about 10 mW. In some applications, single power levels of 1 mW or less are still sensitive to non-linear effects, so that the effective area is still an important consideration in such lower power systems. A long distance could be considered to be an application in which the distance between optical regenerators or repeaters or amplifiers is in excess of 50 km or more. Regenerators are to be distinguished from repeaters that make use of optical amplifiers. Repeater spacing, especially in high data density systems, can be less than half the regenerator spacing. To provide a suitable waveguide for a multiplex transmission, the total dispersion should be low, but not zero, and have a low dispersion slope over the window of operating wavelength.
Generally, an optical waveguide fiber having a large effective area (Aeff) reduces non-linear optical effects, including self-phase modulation, four-wave-mixing, cross-phase modulation, and non-linear scattering processes, all of which can cause degradation of signals in high powered systems. In general, a waveguide fiber having a segmented core can provide a large effective area while limiting the non-linear optical effects.
The mathematical description of these non-linear effects includes the ratio, P/Aeff, where P is the optical power. For example, a non-linear optical effect can be described by an equation containing the term, exp [Pxc3x97Leff/Aeff], where Leff is effective length. Thus, an increase in Aeff produces a decrease in the non-linear contribution to the degradation of a light signal. On the other hand, an increase in effective area of an optical waveguide fiber typically results in an increase in microbending induced losses which attenuate signal transmission through a fiber. The microbending losses become increasingly significant over long distances or spacing between regenerators, amplifiers, transmitters and/or receivers.
Optical amplifier technology and/or wavelength division multiplexing techniques are typically employed in communication systems which require one gigabyte per second and higher transmission rates. Thus waveguide fiber manufacturers have designed waveguides that are less susceptible to non-linear effects induced by higher power signals or by four wave mixing in multiplexing systems. Preferred waveguide fibers have low linear dispersion and low attenuation as well. Furthermore, fiber polarization mode dispersion (PMD) may be a major contributor to overall system PMD. Therefore, a suitable waveguide fiber should also have low PMD. Lower fiber PMD can also provide upgrade paths for high bit rate transmission (e.g. 40 Gbs and higher) in existing or upgraded systems. In addition, the waveguide fiber preferably displays these properties over a particular extended wavelength range in order to accommodate wavelength division multiplexing used for multiple channel transmission.
One aspect of the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber that offers low microbending sensitivity. The fibers disclosed herein preferably include a single segment core. The core region is described by a refractive index profile, a relative refractive index percent, and an outer radius. The optical waveguide fiber further includes a clad layer surrounding and in contact with the core. Unless indicated otherwise, the effective area described herein corresponds to a wavelength of about 1550 nm.
Preferably, the effective area of the fibers disclosed herein is greater than or equal to about 90 xcexcm2, and exhibits microbending of less than or equal to about 3.0 dB/m, more preferably less than or equal to about 2.0 dB/m, even more preferably less than or equal to about 1.5 dB/m, even still more preferably less than or equal to about 1.0 dB/m, yet still more preferably less than or equal to about 0.8 dB/m, and even still more preferably less than or equal to about 0.5 dB/m.
The core region and cladding layer preferably define a step-index refractive index profile. Preferably, the fibers disclosed herein has a maximum relative index xcex941% of between about 0.20% and about 0.35%, more preferably between about 0.24% and about 0.33%, even more preferably between about 0.26% and about 0.32%, and still more preferably between about 0.27% and about 0.31%. Preferably, the core radius of the fibers disclosed herein, measured at half the maximum or peak relative index, is between about 4.0 xcexcm and about 7.0 xcexcm, more preferably between about 4.5 xcexcm and about 6.5 xcexcm, and still more preferably is between about 5.0 xcexcm and about 6.2 xcexcm.
The fibers disclosed herein further preferably comprise a primary coating surrounding the cladding and a secondary coating, also known as an outer primary coating, surrounding the primary coating. The primary coating is preferably selected to have a modulus of elasticity of less than about 5 MPa, more preferably less than about 3 MPa, and even more preferably less than about 1.5 MPa. Preferably, the modulus of elasticity of the secondary coating is greater than 700 Mpa, more preferably greater than 800 Mpa, and even more preferably over 900 MPa.
Preferably, the fibers disclosed herein comprise a core region of silica which is up-doped with germania, and a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure or substantially pure silica.
In another aspect, the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber having a step-index profile. Preferably, the effective area of the fibers disclosed herein is greater than or equal to about 90 xcexcm2. In one or more preferred embodiments, the effective area is between about 90 xcexcm2 and about 115 xcexcm2, more preferably between about 95 xcexcm2 and about 110 xcexcm2.
Preferably, the fibers disclosed herein have a maximum relative index xcex941% of between about 0.20% and about 0.35%, more preferably between about 0.24% and about 0.33%, still more preferably between about 0.26% and about 0.32%, and yet more preferably between about 0.27% and about 0.31%. Preferably, the core radius of the fibers disclosed herein, measured at half the maximum or peak relative index, is between about 4.0 xcexcm and about 7.0 xcexcm, more preferably between about 4.5 xcexcm and about 6.5 xcexcm, even more preferably between about 5.0 xcexcm and about 6.2 xcexcm.
Preferably, the fibers disclosed herein comprise a core region of silica which is up-doped with germania, and a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure, or substantially pure, silica.
The fibers disclosed herein preferably exhibit an attenuation at a wavelength of about 1550 nm of less than or equal to about 0.25 dB/km, more preferably less than or equal to about 0.22 dB/km, even more preferably less than or equal to about 0.2 dB/km, yet more preferably less than or equal to about 0.19 dB/km, and most preferably less than about 0.185 dB/km.
In preferred embodiments, the fibers disclosed herein exhibit a total dispersion at a wavelength of about 1560 nm of preferably within the range of about 16 ps/nm-km to about 22 ps/nm-km, more preferably within the range of about 17 ps/nm-km to about 21 ps/nm-km, and even more preferably within the range of about 18 ps/nm-km to about 20 ps/nm-km.
The total dispersion slope at a wavelength of about 1550 nm of the fibers disclosed herein is preferably less than or equal to about 0.09 ps/nm2-km. In one or more preferred embodiments, the total dispersion slope at a wavelength of about 1550 nm of the fibers disclosed herein is preferably between about 0.045 ps/nm2-km and about 0.075 ps/nm2-km, even more preferably between about 0.05 ps/nm2-km and about 0.07 ps/nm2-km, still more preferably between about 0.055 ps/nm2-km and about 0.065 ps/nm2-km.
In yet another aspect, the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber having a maximum relative index xcex941% of between about 0.20% and about 0.35%, more preferably between about 0.24% and about 0.33%, even more preferably between about 0.26% and about 0.32%, and still more preferably between about 0.27% and about 0.31%. Preferably, the core radius of the fibers disclosed herein, measured at half the maximum or peak relative index, is between about 4.0 xcexcm and about 7.0 xcexcm, more preferably between about 4.5 xcexcm and about 6.5 xcexcm, and still more preferably between about 5.0 xcexcm and about 6.2 xcexcm.
Preferably, the refractive index profile of the fibers disclosed herein is of the step-index type. Preferably, the fibers disclosed herein comprise a core region of silica which is up-doped with germania, and a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure, or substantially pure, silica.
In still another aspect, the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber which comprises an up-doped core region or which comprises a germano-silicate core region or which comprises a germania-doped silica core. Preferably, the fibers disclosed herein comprise a core region of silica which is up-doped with germania surrounded by a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure, or substantially pure, silica. Preferably, the effective area is greater than or equal to about 90 xcexcm2.
In yet another aspect, the optical waveguide fiber disclosed herein relates to a relatively large effective area single mode optical waveguide fiber which exhibits low PMD. Preferably, the effective area is greater than or equal to about 90 xcexcm2. Preferably, the PMD exhibited by the fibers disclosed herein is less than about 0.1 ps/km1/2 (unspun), more preferably less than about 0.08 ps/km1/2 (unspun), even more preferably less than about 0.05 ps/km1/2 (unspun), still more preferably less than about 0.03 ps/km1/2 (unspun), even still more preferably less than about 0.02 ps/km1/2 (unspun). In one preferred embodiment, the optical waveguide fiber disclosed herein relates to a single mode optical waveguide fiber having an effective area greater than or equal to about 90 xcexcm2 and which a PMD of less than about 0.05 ps/km1/2 (unspun). In another preferred embodiment, the optical waveguide fiber disclosed herein relates to a single mode optical waveguide fiber having an effective area greater than or equal to about 90 xcexcm2 and which a PMD of less than about 0.02 ps/km1/2 (unspun).
Preferably, the fibers disclosed herein have a step-index profile, and further preferably comprises a core region of silica, which is up-doped with germania, the core region being surrounded by a cladding of silica. Preferably, the cladding contains no down-dopants. Even more preferably, the cladding contains no fluorine. Most preferably, the cladding comprises pure, or substantially pure, silica.
In another aspect, the optical waveguide fiber disclosed herein relates to an optical waveguide fiber comprising a core having a refractive index profile defined by a radius and a relative refractive index percent, wherein the core contains germania, and a clad layer surrounding and in contact with the core and having a refractive index profile defined by a radius and a relative refractive index percent, wherein the core and the clad layer provide an effective area greater than about 90 xcexcm2, and wherein the fiber contains substantially no fluorine. Preferably, the core and the clad layer provide an effective area of between about 90 xcexcm2 and about 115 xcexcm2, and more preferably the core and the clad layer provide an effective area of between about 95 xcexcm2 and about 110 xcexcm2. In a preferred embodiment, the core and the clad layer provide an effective area of about 101 xcexcm2. Preferably, the core and the cladding define a step-index profile. Preferably, the relative refractive index of the core is within the range of from about 0.20% to about 0.35%, more preferably the relative refractive index of the core is within the range of from about 0.24% to about 0.33%. Preferably, the radius of the core is within the range of from about 4.0 xcexcm to about 7.0 xcexcm, more preferably the radius of the core is within the range of from about 4.5 xcexcm to about 6.5 xcexcm. Preferably, the core has an alpha greater than about 5, and more preferably the core has an alpha between about 7 and about 14. Preferably, the fiber has a cabled cutoff wavelength of less than or equal to about 1500 nm, more preferably the fiber has a cabled cutoff wavelength of between about 1200 nm and about 1500 nm. In a preferred embodiment, the fiber has a cabled cutoff wavelength of between about 1250 nm and about 1400 nm. In another preferred embodiment, the fiber has a cabled cutoff wavelength of between about 1300 nm and about 1375 nm. Preferably, the fiber exhibits macrobending loss less than about 15 dB/m in a 20 mm, 5 turn test, more preferably less than about 10 dB/m in a 20 mm, 5 turn test, and even more preferably less than about 5 dB/m in a 20 mm, 5 turn test. The fiber preferably further comprises a primary coating surrounding the clad layer and a secondary coating surrounding the primary coating. The primary coating preferably has a modulus of elasticity of less than about 5 MPa. The secondary coating preferably has a modulus of elasticity of greater than about 700 MPa. Preferably, the fiber exhibits microbending loss of less than about 3.0 dB/m, more preferably less than about 2.0 dB/m, even more preferably less than about 1.5 dB/m, still more preferably less than about 1.0 dB/m, even still more preferably less than about 0.8 dB/m, and still more preferably less than about 0.5 dB/m. Preferably, the attenuation of the optical fiber at 1383 nm is not more than 0.1 dB/km higher than its attenuation at 1310 nm. More preferably, the attenuation of the optical fiber at 1383 nm is not more than 0.05 dB/km higher than its attenuation at 1310 nm. Still more preferably, the attenuation of the optical fiber at 1383 nm is not more than 0.01 dB/km higher than its attenuation at 1310 nm. Even still more preferably, the attenuation of the optical fiber at 1383 nm is less than or about equal to than its attenuation at 1310 nm. Preferably, the fiber exhibits a PMD of less than about 0.1 ps/km1/2, more preferably less than about 0.05 ps/km1/2, even more preferably less than about 0.01 ps/km1/2, and still more preferably less than or equal to about 0.006 ps/km1/2. Preferably, the fiber exhibits an attenuation at a wavelength of about 1550 nm of less than or equal to about 0.25 dB/km, more preferably less than or equal to about 0.22 dB/km, even more preferably less than or equal to about 0.2 dB/km, and still more preferably less than about 0.185 dB/km. Preferably, the fiber exhibits a total dispersion within the range of about 16 ps/nm-km to about 22 ps/nm-km at a wavelength of about 1560 nm.
In another aspect, the optical waveguide fiber disclosed herein relates to an optical waveguide fiber comprising a core having a refractive index profile defined by a radius and a relative refractive index percent with an alpha greater than about 5, wherein the core contains germania and wherein the relative refractive index of the core is within the range of about 0.20% to about 0.35% and the radius of the core is within the range of from about 4.0 xcexcm to about 7.0 xcexcm., and a clad layer surrounding and in contact with the core and having a refractive index profile defined by a radius and a relative refractive index percent, wherein the fiber contains substantially no fluorine. Preferably, the relative refractive index of the core is within the range of from about 0.24% to about 0.33%. Preferably, the radius of the core is within the range of from about 4.5 xcexcm to about 6.5 xcexcm. Preferably, the core has an alpha between about 7 and about 14. Preferably, the core and the cladding define a step-index profile. Preferably, the fiber further comprises a primary coating surrounding the clad layer, and a secondary coating surrounding the primary coating. The primary coating preferably has a modulus of elasticity of less than about 5 MPa. The secondary coating preferably has a modulus of elasticity of greater than about 700 MPa. Preferably, the attenuation of the optical fiber at 1383 nm is not more than 0.1 dB/km higher than its attenuation at 1310 nm. More preferably, the attenuation of the optical fiber at 1383 nm is not more than 0.05 dB/km higher than its attenuation at 1310 nm. Even more preferably, the attenuation of the optical fiber at 1383 nm is not more than 0.01 dB/km higher than its attenuation at 1310 nm. Still more preferably, the attenuation of the optical fiber at 1383 nm is less than or about equal to than its attenuation at 1310 nm. Preferably, the fiber exhibits a PMD of less than about 0.1 ps/km1/2, more preferably less than about 0.05 ps/km1/2, even more preferably less than about 0.01 ps/km1/2, still more preferably even more preferably less than about 0.006 ps/km1/2.
In another aspect, the optical waveguide fiber disclosed herein relates to an optical waveguide fiber comprising a core having a refractive index profile defined by a radius and a relative refractive index percent, wherein the core contains germania, and a clad layer surrounding and in contact with the core and having a refractive index profile defined by a radius and a relative refractive index percent, wherein the core and the clad layer provide an effective area greater than about 90 xcexcm2, and wherein the fiber exhibits a PMD of less than about 0.1 ps/km1/2.
In another aspect, the optical waveguide fiber disclosed herein relates to an optical waveguide fiber comprising a core having a refractive index profile defined by a radius and a relative refractive index percent, wherein the core contains germania and a clad layer surrounding and in contact with the core and having a refractive index profile defined by a radius and a relative refractive index percent, wherein the core and the clad layer provide an effective area greater than about 90 xcexcm2, and wherein the attenuation of the optical fiber at 1383 nm is not more than 0.1 dB/km higher than its attenuation at 1310 nm.
In another aspect, an optical signal transmission system disclosed herein comprises a transmitter, a receiver, and an optical transmission line optically coupled to the transmitter and receiver, wherein the optical transmission line comprises at least one optical fiber section having a core and a clad layer which define a step-index profile that provides an effective area greater than about 90 xcexcm2, wherein the fiber exhibits an attenuation at 1383 nm which is not more than 0.1 dB/km higher than its attenuation at 1310 nm. The the core preferably contains germania. The fiber section preferably contains substantially no fluorine. Preferably, the fiber section exhibits a total dispersion within the range of about 16 ps/nm-km to about 22 ps/nm-km at a wavelength of about 1560 nm. Preferably, the fiber section exhibits a PMD of less than about 0.1 ps/km1/2. In a preferred embodiment, at least one Raman amplifier is optically coupled to the optical fiber section. Preferably, the system further comprises a multiplexer for interconnecting a plurality of channels capable of carrying optical signals onto the optical transmission line, wherein at least one of the optical signals propagates at a wavelength between about 1300 nm and 1625 nm. In a preferred embodiment, at least one of the optical signals propagates at a wavelength between about 1330 nm and 1480 nm. Preferably, the system is capable of operating in a coarse wavelength division multiplex mode.
Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.